How do i fix this

[103099]

l try to Union my letter Y but the non manifold error is shown.Anyone who knows how to help please hellp me this is my work.

Shapr3D - Project

https://support.shapr3d.com/hc/en-us/requests/new

[Xdrakosha]

The problem is in the center:

These two parts connected with only one edge:

This is exactly whats called non-manifold.

[Fawksey3D]

Appeared as a single object for me so I guess solved.